Radio communications are now widely used, including on moving vehicles or in any busy situations. Hands-free systems are used for such kinds of radio communications to assure traffic safety or any kind of conveniences.
A hands-free system is formed by a radio apparatus, e.g., a cellular phone, and a hands-free apparatus linked to the radio apparatus by a local radio link. Examples of such a local radio link are Bluetooth (TM) and a wireless local area network (WLAN). A standardized hands-free profile to support such kinds of applications is provided in the Bluetooth specifications.
Here is assumed a hands-free system formed by a radio apparatus and a hands-free apparatus. The hands-free apparatus has a microphone, a loud speaker, and an operation panel. The hands-free apparatus is connectable to the radio apparatus by a local radio link, and the radio apparatus may be set normal, i.e., to be used while being held by a human hand, or hands-free. When the radio apparatus is set hands-free, a control channel is established on the local radio link.
The radio apparatus is used as an ending node of a communication network. While the radio apparatus is set hands-free, a call addressed to another ending node of the communication network may be made on the hands-free apparatus by operating the operation panel. The call is transferred to the radio apparatus and then sent to the addressed ending node. The hands-free apparatus and the radio apparatus arrange a voice channel to be established on the local radio link to enable a hands-free voice communication with the addressed ending node.
There may be a case where the call is accepted on the addressed ending node, and no voice channel is established on the local radio link. Such a case occurs due to, e.g., an obstacle that happens to exist between the hands-free apparatus and the radio apparatus and block the wave path of the local radio link. In this case, a connection between the radio apparatus and the addressed ending node has been established on the communication network and may continue being kept and charged while the intended hands-free voice communication is disturbed.
A radio apparatus was improved to alleviate a similar, but not exactly the same problem, and the improved radio apparatus is disclosed in the Japanese published patent applications, e.g., 2002-300648, the English version of which is available on the Japan Patent Office website.
This radio apparatus is used as an ending node of a communication network, and is linked to a hands-free apparatus by a local radio link to form a hands-free system. The radio apparatus establishes a voice channel on the local radio link with the hands-free apparatus, and a connection with a second ending node of the communication network. A hands-free voice communication is thus enabled between the hands-free system and the second ending node. The radio apparatus releases the connection with the second ending node in a case where the performance of the local radio link is deteriorated during the hands-free voice communication.
This conventional technique, however, does not solve the problem that a connection with the second ending node may be established and charged although a voice channel on the local radio link fails to be established and an intended hands-free voice communication is disturbed.